CF: Body Composition Assessment 2020
Click here to see the explanation of recommendation ratings (Strong, Fair, Weak, Consensus, Insufficient Evidence) and labels (Imperative or Conditional). To see more detail on the evidence from which the following recommendations were drawn, use the hyperlinks in the Supporting Evidence Section below.
CF: Dual-Energy X-Ray Absorptiometry (DEXA)
In individuals with cystic fibrosis (CF), it is reasonable for the RDN or international equivalent to assess body composition using dual-energy X-ray absorptiometry (DEXA), when feasible and available, since DEXA is the gold standard in clinical settings.
CF: Single-Site Anthropometric Measures and Nutrition Focused Physical Exam
In all individuals with cystic fibrosis (CF), when body composition assessment with dual-energy X-ray absorptiometry (DEXA) is not feasible or indicated, it is reasonable for the RDN or international equivalent to assess mid-upper arm circumference with single-site skinfold measures and/or Nutrition-Focused Physical Exams at each nutrition assessment in order to aid in the classification of nutrition status over time.
CF: Accuracy of Skinfold Measures and Bioelectrical Impedance Analysis (BIA)
In individuals with cystic fibrosis (CF), when dual-energy X-ray absorptiometry (DEXA) is not feasible or indicated, the RDN or international equivalent may use age-appropriate tests including skinfold measures or bioelectrical impedance analysis (BIA) with caution when tracking body composition over time, understanding that prediction equations using these methods may over- or under-estimate absolute fat and fat-free mass.
Risks/Harms of Implementing This Recommendation
Although very minimal, DEXA provides a small amount of radiation per scan.
Conditions of Application
Indications for DEXA scans. DEXA scans can provide accurate information on bone density and body composition that can aid the RDN in determining nutrition priorities and, consequently, optimal nutrition interventions. Consensus guidelines for individuals with CF specify that individuals with CF should have a DEXA scan beginning at 8 years of age if individuals meet the following indications:(Aris et al 2005, Marquette et al 2016, Sermet-Gaudelus et al 2011, Padula et al 2017)
- Short gut
- Cirrhosis of the liver
- Celiac disease (once tTg normalizes)
- Long bone fracture of lower extremity
- 2 or more upper extremity fractures
- Moderate or severe malnutrition (BMI z-score ≤-2 OR highet z-score ≤-3)
- Compression fracture (must do hip or forearm scan; lumbar scan not accurate in these patients)
- >90 days of systemic glucocorticoid therapy at suppressive doses and/or evidence of glucocorticoid excess
- FEV1 <50%
- FEV1 50-75% with multiple hospitalizations or deteriorating lung function
- Poorly controlled autoimmune disease (i.e. celiac disease, rheumatoid arthritis, inflammatory bowel disease)
- Poorly controlled CF related diabetes
- Pre-organ transplant
Or a combination of three relative indications:
- Well controlled CF related diabetes
- Mild malnutrition (BMI z-score ≤-1) despite nutritional interventions
- Delayed puberty
- Below genetic height potential (stunting)
- Family history of early osteoporosis
- X-ray findings consistent with low bone mineral density
Frequency of DEXA scans. DEXA scans should be repeated:(Aris et al 2005, Marquette et al 2016, Sermet-Gaudelus et al 2011)
- If BMD z-score is between +2 to -1, suggest repeat scan every 5 years or sooner if there are clinical indications.
- If BMD z-score is between -1 and -2, suggest repeat scan every 2 years.
- If BMD z-score is < -2, suggest repeat scan every year.
RDNs may not have the ability to order DEXA scans directly, but can work with the individuals with CF interdisciplinary team to determine when a DEXA scan may improve nutrition assessment and, consequently, treatment for the individual with CF.
Frequency of skinfold measures, MUAC, NFPE and BIA. Alternative methods of measuring body composition may not be validated for the CF population. However, when tracked over time, relative measurements can contribute to a malnutrition diagnosis over time. Therefore, body composition measures with these methods should be assessed at each nutrition assessment (please see Nutrition Assessment section for frequency of nutrition assessment).
Methods for measuring BIA. Given the variability in BIA devices and the sensitivity of BIA to hydration status and timing of meals (e.g, fasting status), the same protocol and testing conditions should be used over time (Kyle et al 2015). Furthermore, manufacturer-provided estimates of fat mass and fat free mass may be based on unknown proprietary equations, thus BIA devices that provide raw parameters, such as reactance and resistance should be used.
Training. All persons conducting body composition measures should be adequately trained using an institution-specific standardized protocol and measurement tools (ex: calipers, measuring tape, BIA equations).
Potential Costs Associated with Application
Costs for a DEXA scan are high and may not be covered by insurance for the sake of body composition alone. However, insurance may cover DEXA scans for bone density, and RDNs can request measures for fat and lean body mass during these scans, though this may not always be an option. Accurate information on bone density and body composition are valuable in nutrition assessment. However, if the DEXA scans are not covered by insurance, RDNs should consider assessment of body composition using alternative methods and track measurements over time to determine relative change. Costs for BIA vary depending on the specific device.
Background. Increased risk of malnutrition in cystic fibrosis (CF) may lead to alterations in body composition, including fat and lean mass as well as bone density. Compared to the general population, individuals with CF have less fat-free mass and bone mineral density (Calella et al 2018), which increases risk for sarcopenia, protein-energy wasting and osteopenia. While BMI is useful for screening for nutrition risk, it does not provide a clear indication of body composition (e.g, fat-free mass, fat mass).
Evidence. There were no studies available to indicate whether body composition, assessed by any means, is useful in predicting hard outcomes in either pediatric or adult individuals with CF.(Academy of Nutrition and Dietetics 2019) However, some cross-sectional studies have suggested that fat-free mass is more strongly associated with lung function than BMI (King et al 2010, Pedreira et al 2005, Sheikh et al 2014, Ionescu et al 2002, Olveira et al 2012, Engelen et al 2012, Ionescu et al 2003). In the general population, fat-free mass is inversely associated with mortality and mediates the association between BMI and mortality (Abramowitz et al 2018).
Although costly techniques such as multi-component modeling, computed tomography, and magnetic resonance imaging are often considered gold standards for assessing in vivo body composition, (Borga et al 2018, Ackland et al 2012, Demerath et al 2014), DEXA may be considered the gold standard to measure bone density and body composition in clinical practice (Marquette et al 2016, Sermet-Gaudelus et al 2011, Buckinx et al 2018, Shepherd et al 2017, Calella et al 2019) given its precision and relative feasibility, practicality, accuracy, and safety. DEXA is often used as the reference method for clinical research.
In validity and reliability studies, for pediatric individuals with CF, there were differences in fat mass and fat-free mass measured by equations utilizing 2 or 4 site skinfold measurements or BIA compared to gold standards. The amount of difference, along with if the mass was overestimated vs underestimated, was variable according to individuals’ sex and body composition (Wells et al 2008, Williams et al 2010, Puiman et al 2004). These findings were in agreement with a 2019 systematic review conducted by Calella, et al, which described that accuracy of skinfold measures and BIA may have limited accuracy if individuals with CF have abnormal hydration status or if appropriate prediction methods are not used (Calella et al 2019, Sheean et al 2019). BIA devices may be multi-frequency or spectroscopy or single frequency, the latter of which is considered to be less accurate. Algorithms/equations used for multi and single frequency BIA are highly specific according to population and disease state (Sheean et al 2019). Multi-frequency BIA estimates were accurate for measuring body composition compared to DEXA if CF-specific equations were used, but evidence was limited to one study with the pediatric population (Charatsi et al 2016).
FFMBIA(kg)= (0.54*RI) + (0.25*W) + (0.07*H) + (0.04*X50)-11.91
Where RI= resistance index=height2/RE50, cm2/Ω; RE50: resistance at 50 kHz, Ω; W: weight, kg; H: height, cm; X50: reactance at 50 kHz, Ω).
In adults with CF, compared to DEXA, assessment of fat-free mass using skinfold measures or BIA with equations intended for the general population under- or overestimated fat free mass by a mean of -3.3 kg to 2.9 kg and, therefore, had low validity (Hollander et al 2005, King et al 2005). Although body composition methods may have limited accuracy for individuals with CF, repeated measures may give an overall picture of trends in body composition changes over time.
There was no evidence to determine if Nutrition Focused Physical Exams (NFPE) or mid upper arm circumference (MUAC) can be used to validly and reliably assess body composition or if it is longitudinally associated with mortality, FEV1 or quality of life in pediatric or adult individuals with CF (Academy of Nutrition and Dietetics 2019). However, since the accuracy and reliability of other methods to assess body composition were unclear, NFPE and MUAC may contribute information regarding changes in nutrition status over time, even though they may not provide quantified values of fat mass or fat fee mass or give specific information about changes in fat free mass compared to fat mass. The Academy and the American Society for Parenteral and Enteral Nutrition suggest use of MUAC in children and adolescents to diagnose malnutrition in the general population (Becker et al 2015), which has the advantage of not relying on prediction equations developed for the non-CF population. Use of raw measures for skinfolds, MUAC, and BIA, in comparison to available age- and sex- and ethnicity-matched reference populations may provide useful information for nutrition assessment and are not limited by unvalidated assumptions of using prediction equations developed in healthy populations. Reference equations are available for anthropometric (skinfold and MUAC) measures across all ages (Addo et al 2010, World Health Organization 2020, World Health Organization 2020). Various population reference values for raw bioimpedance parameters are also available (Schmidt et al 2019, Mattiello et al 2019, Kuchnia et al 2017), although specific BIA devices are variable.
Recommendation Strength Rationale
The evidence supporting the recommendations regarding measuring body composition with DEXA or BIA had Grade III (limited/weak) evidence in the pediatric population with CF and Grade II (fair) evidence in the adult population with CF. Guidance for indications and frequency for DEXA scans are based on external consensus guidelines. In the systematic review supporting this guideline, the workgroup investigated the validity and reliability as well as the longitudinal relationship with hard outcomes for NFPE, but there were no studies meeting inclusion criteria that examined this assessment method. Therefore, the consensus recommendation was based on clinical expertise.
- Risks/Harms of Implementing This Recommendation
The recommendations were created from the evidence analysis on the following questions. To see detail of the evidence analysis, click the blue hyperlinks below (recommendations rated consensus will not have supporting evidence linked).
In participants with CF, what is the longitudinal relationship (at least 3 months) between body composition and hard outcomes (FEV1, Quality of Life or mortality)?
In pediatric participants with CF, which body composition parameters are valid and reliable compared to reference standards, as measured by validity and/or reliability studies?
In adults with CF, which body composition parameters are valid and reliable compared to reference standards, as measured by validity and/or reliability studies?
Charatsi A, Dusser P, Freund R, Maruani G, Rossin H, Boulier A, Le Bourgeois M, Chedevergne F, de Blic J, Letourneur A, Casimir G, Jais J, Sermet-Gaudelus I. Bioelectrical impedance in young patients with cystic fibrosis: Validation of a specific equation and clinical relevance. Journal of Cystic Fibrosis 2016; 15:825-833
Murphy A, Buntain H, Wong J, Greer R, Wainwright C, Davies P. The use of air displacement plethysmography in children and adolescents with cystic fibrosis. European Journal of Clinical Nutrition 2004; 58:985-9
Puiman P, Francis P, Buntain H, Wainwright C, Masters B, Davies P. Total body water in children with cystic fibrosis using bioelectrical impedance. Journal of Cystic Fibrosis 2004; 3:243-7
Wells G, Heale L, Schneiderman J, Wilkes D, Atenafu E, Coates A, Ratjen F. Assessment of body composition in pediatric patients with cystic fibrosis. Pediatric Pulmonology 2008; 43:1025-32
Williams J, Wells J, Wilson C, Haroun D, Lucas A, Fewtrell M. Evaluation of Lunar Prodigy dual-energy X-ray absorptiometry for assessing body composition in healthy persons and patients by comparison with the criterion 4-component model. The American Journal of Clinical Nutrition 2006; 83:1047-54
Williams J, Wells J, Benden C, Jaffe A, Suri R, Wilson C, Fewtrell M. Body composition assessed by the 4-component model and association with lung function in 6-12-y-old children with cystic fibrosis. American Journal of Clinical Nutrition 2010; 92:1332-43
Hollander F, De Roos N, De Vries J, Van Berkhout F. Assessment of nutritional status in adult patients with cystic fibrosis: whole-body bioimpedance vs body mass index, skinfolds, and leg-to-leg bioimpedance. Journal of the American Dietetic Association 2005; 105:549-55
King S, Wilson J, Kotsimbos T, Bailey M, Nyulasi I. Body composition assessment in adults with cystic fibrosis: comparison of dual-energy X-ray absorptiometry with skinfolds and bioelectrical impedance analysis. Nutrition (Burbank, Los Angeles County, Calif.) 2005; 21:1087-94
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